NW Iberian Research Articles

A New Algorithm Using Support Vector Machines to Detect and Monitor Bloom-Forming Pseudo-nitzschia from OLCI Data

Pseudo-nitzschia spp. blooms are a recurrent problem in many coastal areas globally, imposing some significant threats to the health of humans, ecosystems and the economy. Monitoring programmes have been established, where feasible, to mitigate the impacts caused by Pseudo-nitzschia spp. and other harmful algae blooms. The detection of such blooms from satellite data could really provide timely information on emerging risks but the development of taxa-specific algorithms from available multispectral data is still challenged by coupled optical properties with other taxa and water constituents, availability of ground data and generalisation capabilities of algorithms. Here, we developed a new set of algorithms (PNOI) for the detection and monitoring of Pseudo-nitzschia spp. blooms over the Galician coast (NW Iberian Peninsula) from Sentinel-3 OLCI reflectances using a support vector machine (SVM). Our algorithm was trained and tested with reflectance data from 260 OLCI images and 4607 Pseudo-nitzschia spp. match up data points, of which 2171 were of high quality. The performance of the no bloom/bloom model in the independent test set was robust, showing values of 0.80, 0.72 and 0.79 for the area under the curve (AUC), sensitivity and specificity, respectively. Similar results were obtained by our below detection limit/presence model. We also present different model thresholds based on optimisation of true skill statistic (TSS) and F1-score. PNOI outperforms linear models, while its relationship with in situ chlorophyll-a concentrations is weak, demonstrating a poor correlation with the phytoplankton abundance. We showcase the importance of the PNOI algorithm and OLCI sensor for monitoring the bloom evolution between the weekly ground sampling and during periods of ground data absence, such as due to COVID-19.

Coastal upwelling systems as dynamic mosaics of bacterioplankton functional specialization

Coastal upwelling areas are extraordinarily productive environments where prokaryotic communities, the principal remineralizers of dissolved organic matter (DOM), rapidly respond to phytoplankton bloom and decay dynamics. Nevertheless, the extent of variability of key microbial functions in such dynamic waters remains largely unconstrained. Our metatranscriptomics analyses of 162 marker genes encoding ecologically relevant prokaryotic functions showed distinct spatial-temporal patterns in the NW Iberian Peninsula upwelling area. Short-term (daily) changes in specific bacterial functions associated with changes in biotic and abiotic factors were superimposed on seasonal variability. Taxonomic and functional specialization of prokaryotic communities, based mostly on different resource acquisition strategies, was observed. Our results uncovered the potential influence of prokaryotic functioning on phytoplankton bloom composition and development (e.g., Cellvibrionales and Flavobacteriales increased relative gene expression related to vitamin B12 and siderophore metabolisms during Chaetoceros and Dinophyceae summer blooms). Notably, bacterial adjustments to C- or N-limitation and DMSP availability during summer phytoplankton blooms and different spatial-temporal patterns of variability in the expression of genes with different phosphate affinity indicated a complex role of resource availability in structuring bacterial communities in this upwelling system. Also, a crucial role of Cellvibrionales in the degradation of DOM (carbohydrate metabolism, TCA cycle, proteorhodopsin, ammonium, and phosphate uptake genes) during the summer phytoplankton bloom was found. Overall, this dataset revealed an intertwined mosaic of microbial interactions and nutrient utilization patterns along a spatial-temporal gradient that needs to be considered if we aim to understand the biogeochemical processes in some of the most productive ecosystems in the world´s oceans.

Archaeologiques of sight: The visual world fosters the engagement between doing, seeing, and thinking

The paper examines how materializations of human practices relate to human cognition and to socio-cultural contexts. By combining evidence on the relationship between material culture and perceptual behaviour, we aim to understand the interactions between the mind, objects, and the world. The research is based on data regarding the visual perception of prehistoric pottery that was analyzed using Eye-Tracking techniques in a way that has not been applied previously to archaeological material culture. The datasets come from Galicia (NW Iberian Peninsula) and range from the Middle Neolithic until the end of the Iron Age (6000–200 BP). They belong to very different contexts that comprise a long-term history through diverse socio-cultural formations. A rigorous methodology makes it possible to unveil cross- and intra-cultural patterns of visual response to materiality, while avoiding presentism and subjective bias. The results provide new insights into the agency of material culture, which contribute to our understanding of the relationship between the mind and the material world, and account for the transitive engagement between the way of thinking, seeing, and making things.

Red tides in the Galician rías: historical overview, ecological impact, and future monitoring strategies.

The Galician rías (NW Iberia, Spain) are coastal embayments at the northern boundary of the Canary Current upwelling system. Their favourable conditions for phytoplankton growth turn them into a suitable area for the development of aquaculture activities and a site of most of the national shellfish production. Phytoplankton blooms, a natural phenomenon inside the rías, under certain conditions eventually lead to seawater discolourations (colloquially known as "red tides"). Because of their transient nature, available records derive mainly from opportunistic samplings or casual observations, and are scattered in the literature. As a rule of thumb, red tides in the NW Iberian Peninsula are of non-toxic nature and are not systematically monitored. However, in recent years striking exceptions such as those of the toxic dinoflagellate Alexandrium minutum, a producer of paralytic shellfish toxins, have been registered. The present study goes through a historical overview of red tides in the Galician rías, describing their colouring, responsible organisms, seasonal and geographical occurrence, and their association with other features (harmful algal blooms, biotoxins and shellfish harvesting closures, bioluminescence, etc.), ending with social challenges and proposals for improving the monitoring of red tides in the future.

Tracking fluorescent tracer to monitor grain size-selective dispersion in subtidal zone: Patos Beach case study (NW Iberian Peninsula)

Sediment tracer studies have become an increasingly used and improved technique. This approach allows to evaluate the sediment dispersion and track their pathways in a real marine environment. This type of study is essential to improve current coastal morphodynamic models since questions such as 'Where does the sand nourishment go?' are complex to answer, but essential for improving coastal management. The goal of this work is to analyze the behavior of fluorescent sediment tracers with heterometric grain size distributions in Patos Beach (Ria de Vigo, NW Spain). A field experiment was performed between 24th of September and 22nd of October 2018 with the injection of 200 kg of fluorescent tracer of native sediment in the subtidal zone. Oceanographic and topobathymetric data were acquired, and daily bed sediment samples were taken in order to observe tracer advection and dispersion. The results obtained on this beach allowed the establishment of selective sediment transport at two spatial scales: tracer transport towards the beach and tracer organization around bedforms. This research contributes to improve the current knowledge of sediment transport in a natural environment and its relationship with wave nonlinearities.

Experimental evidence of mate choice as the driving mechanism behind negative assortative mating for shell colour in a marine snail

Abstract How colour polymorphisms are maintained in natural populations constitutes a key subject of study for evolutionary ecologists. One of the mechanisms that has been put forward to explain this phenomenon is negative frequency-dependent selection, which can be caused by different mechanisms. Among these mechanisms is mate choice, or the selection as a potential mate of the rare or dissimilar colour morph by the choosy sex of a given species. In the context of colour polymorphism, mate choice predicts the occurrence of a negative assortative mating pattern, whereby different colour morphs mate more often than expected by chance alone. However, negative assortative mating can also result from other mechanisms, making it, at best, a fallible indicator of a mate choice-driven negative frequency-dependent selection. For this reason, experimental evidence explicitly connecting such a mating pattern to mate choice is necessary to claim that a particular colour polymorphism is being maintained by negative frequency-dependent selection. Here we present experimental evidence backing this relationship for the colour polymorphic marine gastropod Littorina saxatilis from the Ría de Vigo (NW Iberian Peninsula), although how specifically these organisms choose their mates remains unclear. This calls for further experimental efforts to clarify this issue and its relationship to the maintenance of colour polymorphism in L. saxatilis.

Disruptions caused by invasive species and climate change on the functional diversity of a fish community

As the effects of climate change continue to intensify, non-native species are becoming more prevalent in estuarine ecosystems. This has implications for the taxonomic and functional diversity of fish communities. Historically, biodiversity has been a synonym of taxonomic diversity, however this approach often fails to provide accurate insights on ecosystem functioning and resilience. To better understand how climate change is impacting fishes and their traits’ composition, a long-term dataset from Minho Estuary (NW Iberian Peninsula) fish assemblage was analyzed. The results suggest that climate change and extreme weather events altered the prevailing trait modalities of fishes, which led to the overall decrease in functional diversity of the fish assemblage over the course of a decade. This decrease is associated to the loss of some trait modalities that are exclusively found in native species. On the other hand, the invasive species added novel traits associated with the conditions of high temperatures and low precipitation regime currently observed in the studied area. Our results highlight that the shift in the presence and dominance of some traits is directly influenced by climatic changes. Also, despite the addition of novel modalities by the invasive species, the fish assemblage is now less functional and taxonomically diverse than previously. Graphical abstract

Seasonal upwelling influence on trophic indices of mesozooplankton in a coastal food web estimated from δ15N in amino acids

Mesozooplankton communities in upwelling ecosystems are known to be influenced by seasonal upwelling enhancing primary productivity. However, the extent to which changes in trophic dynamics of mesozooplankton are driven by variations in the baseline of nitrogen or in the trophic position (TP) is poorly understood. We used nitrogen stable isotopes (δ15N) in bulk and in specific amino acids (CSIA-AA), as well as the taxonomic composition of mesozooplankton samples collected monthly during two full years, to investigate whether the upwelling intensity affects the isotopic N baseline and other trophic indices at the community level in the coastal system off NW Iberian Peninsula. We hypothesized that enhanced phytoplankton productivity during upwelling events would lead to a shorter and more efficient food web. Upwelling induced mesozooplankton herbivory (by increasing the abundance and biomass of omnivorous-herbivorous copepods and other taxa), resulting in a linear decrease of TPGlx (estimated using Glx = glutamic acid + glutamine, which mainly involves metazoan links) from downwelling to upwelling situations. In contrast, TPAla (estimated using alanine, which also reflects microbial trophic pathways) was highest in low-moderate upwelling and decreased with upwelling strength. Thus, an optimal coupling between metazoan and microbial food webs was reached at low-moderate upwelling intensities when the microbial contribution was ca. 25 %, while this contribution decreased (<15 %) either during downwelling or during strong upwelling. However, the significance of differences in mean values of TP and zooplankton composition was small due to the rapid succession of upwelling and downwelling events. Our results illustrate how a combination of CSIA-AA and community data can provide valuable information on rapid changes in mesozooplankton food web structure in highly dynamic upwelling systems.

Distinctive Accumulation Patterns of Trace Elements in Sediments of Bedrock Rivers (Miño River, NW Iberian Peninsula)

Sediment compositions and enrichment patterns are investigated in an urban reach of a bedrock river, the Miño River passing through Ourense City, Spain. This study focuses on the trace element distribution in different fractions to gain insights into trace element enrichment. To assess enrichment, a context-specific approach was employed, based on the mean, the standard deviation of the estimated background, and the empirical rule, avoiding the pitfalls of general and arbitrary thresholds. Notably, the &lt;0.063 mm and &lt;2 mm fractions showed differential accumulation patterns. Both fractions serve to detect enrichments that can be indicative of contamination, but they measure different things, the maturity of sediments and postdepositional processes being key factors in understanding the sediment composition and enrichments. These findings also highlight the role of rock cavities, particularly those hosting permanent deposits, as traps for trace elements and their potential significance in assessing environmental enrichment. This work contributes to understanding sediment compositions and enrichment dynamics in bedrock rivers. It also underscores the significance of considering site-specific approaches for enrichment assessment and the necessity for further research to unravel the mechanisms driving differential accumulation within distinct depositional environments.

Contrasting appinites, vaugnerites and related granitoids from the NW Iberian Massif: insight into mantle and crustal sources

Abstract. Post-collisional Mg–K-rich mafic rocks with associated granitoids appear regularly in most orogens. They are relevant to evaluate the mantle role in the genesis of granitoids and thereby of the continental crust itself. The most characteristic Mg–K mafic rocks in the Variscan Iberian Massif are appinites and vaugnerites. Two examples with associated granitoids from NW Iberia have been compared to assess their mantle and crustal sources and the magmatic processes involved in their formation. Related granitoids are tonalites, granodiorites and monzonitic granites. Available whole-rock major and trace element compositions, as well as Sr and Nd isotopes, were used for this comparison, along with new Sr–Nd isotopic data. The appinite–granitoid association is calc–alkalic, whereas the vaugneritic one is calc–alkalic transitional to alkali–calcic. Vaugnerites are more enriched in Mg and K, compatible and incompatible trace elements and display more fractionated rare-earth element (REE) patterns than appinites. Associated granitoids provide similar differences. Appinites and vaugnerites have Sr and Nd crustal isotopic signatures resulting from partial melting of a different subduction-type metasomatised mantle: amphibole spinel lherzolites for appinites and more refractory and deeper amphibole phlogopite ± garnet peridotites for vaugnerites. Further interaction of these basic melts with coeval granitoids occurred during their ascent and emplacement. The monzonitic granites derived from partial melting of metaigneous acid granulites, without discarding contribution of metasediments and/or an increasing role of biotite incongruent melting in those related to vaugnerites. An assimilation with fractional crystallisation process between appinite magmas and granulites could explain tonalites and granodiorites. This process was not confirmed for granodiorites related to vaugnerites.

Geochemical dynamics of phosphorus and metals in sediments of a shallow coastal lake (Xuño Lake, Galicia-NW Iberian Peninsula)

The shallow lakes are important freshwater ecosystems, since they support much of biodiversity and ecosystem services of life on land. Shallow lakes are highly dynamic ecological entities that can exist in several alternative stable states through regime shift caused by a natural or human disturbance that exceeds ecological thresholds for biological communities composition and structure equilibria. The sediment as a reservoir has a key role in the limnological regulation of wetlands linked to the fluxes of nutrients and elements in the biogeochemical interplay with the water and macrophytes. For this reason, the role of sediment in the limnology of the shallow coastal lake of Xuño (NW Iberian Peninsula) was explored by seasonally monitoring the chemical composition of water and sediments, also according to macrophyte species. The shallow depth determines the high availability of light in the bottom and a well-mixed water column maintain the surface of the water–sediment interface oxygenated. The oxic conditions of the bottom implies a top-down regulation of the water column in the Xuño shallow lake that limits the diffusion of phosphorus and trace metals (Fe, Mn, Cu, and Co) to the water, buffering eutrophication or contamination levels by immobilization in the sediments. In fact, the concentration of Hg in the lake water in spring, and also its bioavailability, are high due to its release from the sediment in suboxic conditions. The cover of helophyte species Phragmites Australis and Schoenoplectus Lacustris showed differences in the assimilation of organic monoester and diester phosphorus forms in the sediment. However, the water of the Xuño Lake shows an eutrophic status by the nutrient input associated with the birds populations as indicated by microbiological data.

Interpretation of Funerary Spaces in Roman Times: Insights from a Nucleus of Braga, NW Iberian Peninsula

The funerary/cult archeological nucleus of Rua do Raio (Braga, in the northwest of the Iberian Peninsula) was discovered between 2007 and 2009, under the excavation works of a necropolis of Bracara Augusta. This building exhibits a set of particularities that confirms its archeological importance. It is a construction dating from the middle of the 1st century AD, subject to two reforms, one in the second half of the 1st century AD and another in the 2nd century AD, with a trapezoidal shape and comprising ten rectangular tanks rendered with opus signinum mortars. It shows a unique architectural configuration in the city, as well as in the Portuguese territory, and the space is under musealization, together with a set of graves identified in the same archeological intervention. The present investigation contextualizes the funerary and religious architecture of the city. Its description is presented, highlighting its relevance, and an interpretative possibility is formulated.

Assessing high resolution thermal monitoring of complex intertidal environments from space: The case of ECOSTRESS at Rias Baixas, NW Iberia

Currently, thermal sensors on satellites and other orbital platforms with high spatial resolution designed to monitor the oceans are often insufficient to assess the surface temperature of small bodies of water or within the coastal boundary layer. As the accuracy and sensitivity of remote sensing satellites improve, the demand for more accurate and up-to-date basic data sets for calibration increases. The quality of the thermal data collected by ECOSTRESS on the International Space Station allows the characterization of thermal stress levels in coastal ecosystems with a high spatial resolution of 70 m and a return time from hours to 5 days. This study focused on the calibration of ECOSTRESS estimates with in situ surface temperature data from sensors installed at 3 cm depth in the sediment on the intertidal muddy sandflats of three of the Rías Baixas in Galicia, NW Iberian Peninsula, from 2019 to 2021. A final number of 45 ECOSTRESS temperature images were analyzed. From these, 20% contained substantial georeferencing errors which had to be corrected manually with GIS software tools. We applied the Fourier's law of Heat Conduction to derive surface estimates from loggers sub-surface measurements that could be directly compared with ECOSTRESS data. Overall, a good calibration which explained more than 80% of ECOSTRESS temperature estimates for the whole dataset was obtained, but with an intrinsic cold bias around 1.39 °C. When temperatures at a depth of 3 cm were used, the linear fit became worse and the negative bias increased to 1.49 °C. Closer inspection revealed that night measurements were responsible for this larger deviation, as ECOSTRESS estimates became much colder compared to within sediment measurements because of the combined effect of the instrument intrinsic bias and nocturnal surface cooling. The best calibration was obtained when surface estimates were calculated just for the nighttime, as the cold bias decreased to 0.93 °C. More importantly, during hot daytime conditions in emersion above 20 °C, ECOSTRESS data matched surface temperature estimates, probably because of a better performance of ECOSTRESS algorithm at dry surfaces with lower emissivity. Thus, during the most ecologically relevant periods when high temperatures could drive thermal stress in many commercially-important bivalve species, ECOSTRESS provides accurate surface estimates that can be used to derive sub surface temperatures at the depths at which the different burrowing organisms live. We thus conclude that this instrument constitutes an important global tool to examine thermal stress at an unprecedented spatial scale for complex sea-land boundary systems.

Insights into the fauna associated with Egeria densa at the upper section of the international Minho River estuary (NW Iberian Peninsula) 3 decades after its establishment

The macrophyte Egeria densa Planchon, 1849 is a freshwater plant native to the subtropical regions of South America. Fast vegetative reproduction and efficient dispersal allow this species to form extensive beds that produce high levels of oxygen in freshwater ecosystems, generating microhabitats that act as refuge and nursery for an array of organisms, increasing sedimentation and light availability. Despite its undisputable ecological role, it is considered invasive and is present on all continents except Antarctica with the first records in Europe occurring at the 20th century. At the international Minho River (NW Iberian Peninsula), the observation of its presence was noted in the 1990s and is now an established population in this ecosystem. This study is the first descriptive-taxonomical assessment of the associated fauna with the exotic macrophyte E. densa, using both morphological and molecular approaches, three decades after its establishment in the international Minho River. Results indicate the presence of a faunal assemblage, composed a total of 20 identified species, including platyhelminths, hydrozoans, bryozoans, molluscs (Gastropoda), annelids (Oligochaeta and Hirudinea), crustaceans (Ostracoda, Copepoda, Branchiopoda and Amphipoda), aquatic mites and insects. Paludicella aff. articulata (Ehrenberg, 1831), Girardia sinensis Chen & Wang, 2015, Lebertia insignis Neuman, 1880 and Ceriodaphnia rigaudi Richard 1894 are recorded for the first time in Portugal.

Understanding seismicity and seismotectonics in a stable continental region (NW Iberian Peninsula): Implications for the nature of intraplate seismicity

Despite that earthquakes in stable continental regions (SCR) often cause more damage than interplate seismicity, they remain poorly understood. This is mainly because of the lower rate of intraplate seismicity and because of its different behaviour compared to the better-known seismicity at the plate boundary. Understand the characteristics of the intraplate seismicity is a challenge for the seismic risk studies. We study and characterise an SCR (NW Iberian Peninsula), which not only registers moderate instrumental intraplate seismicity, but also important historic seismicity and paleoseismic activity. To tackle some of the difficulties posed by intraplate seismicity, we analyse a wide and multidisciplinary data set (e.g., geological structures, seismicity, focal mechanisms, and geophysical data). Seismicity in this region is not associated with an old rift, but with inherited faults widely distributed throughout the region with a great variety of orientations. The reactivation kinematics of these faults are coherent with the current regional stresses. Instrumental seismicity is not associated with the large active faults nor with crustal limits. Seismicity is mainly clustered in swarms and sequences. Although seismic swarms present lower magnitudes, they are the most common. Based on swarms' characteristics (high b-values, upward spatiotemporal migration), reported mantellic CO2 in some thermal springs, and the reactivation of inherited steeply-dipping faults, we propose the migration of deep fluids through steeply-dipping fractured areas as the cause of the intraplate seismicity. These processes could increase the pore pressure and decrease the stresses necessary for the fault rupture in a fault-valve behaviour. In general, in intraplate context, the important control in the seismicity of the inherited fault systems favourable oriented under the current stress tensor is observed, and also the need for mechanisms that can decrease the effective stress for the fault ruptures. Mechanisms as hydrothermal fluids in arterial faults with fault-valve processes has been identified as an effective driver of intraplate seismicity, playing an important role in stability of tectonic faults. The large number and variety of these faults, that share the low strain rates in intraplate polyorogenic context, may explain the different characteristics of these intraplate regions compared with the interplate regions, as the “unanticipated” behaviour, variety of kinematics, the long quiescence periods without seismicity associated and erosion obliterating their morphotectonic expression.

Hydrozoans (Cnidaria) from the estuarine zone of the International Minho River, NW Iberian Peninsula, Atlantic Europe

In environmental impact studies conducted in coastal regions, the survey of biodiversity is crucial in areas that are subject to interventions. As the characterization of aquatic invertebrates may indicate important issues that need to be addressed. In this regard, hydrozoans (Class Hydrozoa, Phylum Cnidaria) are recognised as important bioindicators. These organisms are characterized by biradial, tetramerous, or polymerous symmetry, a simple gastrovascular system, and non-cellular mesoglea. The aim of the present study was to perform the first descriptive survey of hydrozoan species found in the estuary of the International Minho River (shared by Portugal and Spain), which is classified as an Important Bird Area and is a site of the Natura 2000 network. Specimens were collected from the tidal marine, brackish and tidal freshwater wetland zones through 1) glass eel fishing bycatch using stow nets at flood tides around the new moon (length of float lines: 10 m; bottom anchored lead line: 15 m; height: 8 m; mesh size: 1–2 mm); 2) beam trawl fishing (bottom trawling for 10 min), including species associated with bivalves; 3) Van Veen grab sampler for sediment sampling; 4) on wood fragments in the saltmarsh of the Coura River (tributary of the Minho River); and 5) individuals on the leaves of aquatic plants. A total of 19 species were identified, four of which were first occurrences for Portugal, six for the mainland coast of the country, and one for Southern Europe [Diphasia fallax (Johnston, 1847)]. Three neotypes are also proposed for the species Hydra viridissima, Hydra oligactis and Gymnangium montagui based on the criteria of the International Commission on Zoological Nomenclature. As these organisms are considered bioindicators, the diversity of the hydrozoan community in the Minho River may indicate good water quality.

Colonization in Artificial Seaweed Substrates: Two Locations, One Year

Artificial substrates have been implemented to overcome the problems associated with quantitative sampling of marine epifaunal assemblages. These substrates provide artificial habitats that mimic natural habitat features, thereby standardizing the sampling effort and enabling direct comparisons among different sites and studies. This paper explores the potential of the “Artificial Seaweed Monitoring System” (ASMS) sampling methodology to evaluate the natural variability of assemblages along a coastline of more than 200 km, by describing the succession of the ASMS’ associated macrofauna at two Rías of the Galician Coast (NW Iberian Peninsula) after 3, 6, 9, and 12 months after deployment. The results show that macrofauna assemblages harbored by ASMS differ between locations for every type of data. The results also support the hypothesis that succession in benthic communities is not a linear process, but rather a mixture of different successional stages. The use of the ASMS is proved to be a successful standard monitoring methodology, as it is sensitive to scale-dependent patterns and captures the temporal variability of macrobenthic assemblages. Hence, the ASMS can serve as a replicable approach contributing to the “Good Environmental Status” assessment through non-destructive monitoring programs based on benthic marine macrofauna monitoring, capturing the variability in representative assemblages as long as sampling deployment periods are standard.

Short-Term Interactions of Noctiluca scintillans with the Toxic Dinoflagellates Dinophysis acuminata and Alexandrium minutum: Growth, Toxins and Allelopathic Effects.

The Galician Rías (NW Iberian Peninsula) are an important shellfish aquaculture area periodically affected by toxic episodes often caused by dinoflagellates such as Dinophysis acuminata and Alexandrium minutum, among others. In turn, water discolorations are mostly associated with non-toxic organisms such as the heterotrophic dinoflagellate Noctiluca scintillans, a voracious non-selective predator. The objective of this work was to study the biological interactions among these dinoflagellates and their outcome in terms of survival, growth and toxins content. To that aim, short experiments (4 days) were carried out on mixed cultures with N. scintillans (20 cells mL-1) and (i) one strain of D. acuminata (50, 100 and 500 cells mL-1) and (ii) two strains of A. minutum (100, 500 and 1000 cells mL-1). Cultures of N. scintillans with two A. minutum collapsed by the end of the assays. Both D. acuminata and A. minutum exposed to N. scintillans arrested its growth, though feeding vacuoles in the latter rarely contained any prey. Toxin analyses at the end of the experiment showed an increase in intracellular OA levels in D. acuminata and a significant reduction in PSTs in both A. minutum strains. Neither OA nor PSTs were detected in N. scintillans. Overall, the present study indicated that the interactions among them were ruled by negative allelopathic effects.

Trophic ecology of Octopus vulgaris paralarvae along the Iberian Canary current eastern boundary upwelling system

Our knowledge of the diet of wild octopus paralarvae, Octopus vulgaris, is restricted to the first 2 weeks of its planktonic phase when they are selective hunters found near the coastline. These small paralarvae, bearing only three suckers per arm, are transported by oceanic currents from the coast towards offshore waters, where they complete the planktonic phase over 2 months. Here, we have investigated the trophic ecology of O. vulgaris paralarvae in two contrasting upwelling sub-regions of the Iberian Canary current (ICC) eastern boundary upwelling system and have evaluated dietary change as paralarvae develop (inferred by counting the number of suckers per arm, ranging from three to 15) along the coastal-oceanic gradient during their planktonic phase. Using high-throughput amplicon sequencing, we have characterised the diet of 100 paralarvae collected along the Northwest Iberian Peninsula (n = 65, three to five suckers per arm) and off the west coast of Morocco (n = 35, three to 15 suckers per arm), identifying up to 87 different prey species. The diet of paralarvae varied along the ICC, with crabs (53.4%), siphonophores (12.2%), copepods (12.3%), cnidarians (8.4%) and pteropods (3.7%) accounting for 90% of the variability detected off NW Iberian Peninsula, whereas off W Morocco, crabs (46.2%), copepods (23.1%), cnidarians (12.9%), krill (9.3%) and fishes (4.2%) explained 95.6% of the variability observed using frequency of observance (FOO%) data. Ontogenetic changes in the diet based on groups of paralarvae with similar numbers per arm were evidenced by the decreasing contribution of coastal meroplankton and an increase in oceanic holoplankton, including siphonophores, copepods, pteropods and krill. Trophic niche breadth values ranged from 0.06 to 0.67, with averaged values ranging from 0.23 to 0.33 (generalist = 1 and specialist = 0), suggesting that O. vulgaris paralarvae are selective predators through their ontogenetic transition between coastal and oceanic environments.

Taphonomy and dissolution rates of the razor clam Ensis magnus shells: Current status and projected acidification scenarios

The analysis of the natural variability of seawater (Ta, Ωaragonite and pCO2) at Rodas Beach (NW Iberian Peninsula, Spain) revealed an increase of acidification. However, such pH change was not linked to any detrimental effect of the shell taphonomic characteristics of live razor clams harvested during distinct temporal series (length, thickness, organic content or strength). Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would limit the individual characterization. Modelled trends in pH (and Ωaragonite) showed a significant decrease in the last 20 years, despite Ω > 1. Therefore, more recent shells are being secreted in a progressively less saturated carbonate environment and, consequently, more prone to suffer dissolution (and weakening) in projected climatic scenarios. When shells of harvested razor clams were exposed to projected climatic scenarios in the laboratory, dissolution rates were significantly greater for cold-acidic scenarios (more corrosive) as compared to warm-acidic. The median dissolution time (DT50) for shells under the cold-acidic scenario was reduced by half (15 years) when compared to the values observed for shells under current water chemistry conditions (30 years).Galician coastline, often characterised by pCO2-rich and cold waters due to upwelling system, would represent the most corrosive scenario for the shells according to the responses monitored in our survey which highlight future compromise for the ecosystem services supplied by these hard skeletons. Future climate scenarios might condition performance of bivalves but also more complex processes related to carbonate structures. Local biodiversity may be lowered which may reduce the possibility that many species find shelter and feeding grounds, diminishing the optimal substrate for other organisms as needed elements for optimal services in the ecosystems.